This application claims priority of Korean Application No. 2001-31536 filed on Jun. 5, 2001 in the Korean Patent Office, the entire content of which is incorporated herein by reference.
The present invention relates to an electron gun for a cathode ray tube (CRT) and more particularly, to an electron gun that improves the electron beam focusing property while maintaining proper voltage withstanding property by improving the structure of the focus electrode.
Generally, a color projection display system comprises red R, green G and blue B monochrome CRTs. The mono colors from the CRTs are simultaneously projected toward a screen by an optical system, thereby realizing a full-color image.
In such a display system, the luminescence of each of the monochrome CRTs should be enhanced to improve the brightness and definition of the image display on the screen. Therefore, the electron gun of the CRT emits electron beams having a relatively high current density, and each electrode of the electron gun is designed to be applied with a relatively high voltage to form electron lenses.
Accordingly, since the electron gun used for the projection display should be designed to a high current density to realize an optimal spot diameter of an electron beam, it needs a good focus property for converging the electron beams. The electrodes of the electron gun are required to have a high voltage withstanding property so that a short circuit is not occurred by an arc discharge.
To improve the focus property of the electron gun, a diameter of an electron beam-passing aperture for forming a main electron lens is enlarged.
U.S. Pat. No. 4,271,374 (""374 patent) discloses an electron gun having a first cylindrical electrode having a diameter proximal to an inner diameter of a neck portion of a CRT and a second cylindrical electrode, a part of which is disposed within the first cylindrical electrode. This structure is to minimize the spherical aberration of an electron lens while not increasing the diameter of the neck portion of the CRT.
However, in the electron gun of the ""374 patent, since the second cylindrical electrode has a cup-shape, the surface area of the second cylindrical electrode, which faces the first electrode, is increased. This increases the possibility of generating an arc discharge by the high voltage (anode voltage or focus voltage), deteriorating the voltage withstanding property.
Japanese laid-open patent No. 2000-277033 discloses an electron gun for improving the voltage withstanding property. That is, a final focus electrode (to which a focus voltage is applied) disposed in a final accelerating electrode (to which an anode voltage is applied) is designed to be inclined in a longitudinal direction of the electron gun to minimize the surface area facing the final accelerating electrode. As a result, the spacing distance between the final accelerating electrode and the final focus electrode is widened.
Although the voltage withstanding property can be improved by the widened space between the electrodes, the spherical aberration is increased, deteriorating the focus property as the equipotential surface formed by the inclined final focus electrode is steeply varied along the inclined surface of the final focus electrode.
One embodiment of the present invention provides an electron gun that improves the electron beam focusing property while maintaining proper voltage withstanding property by improving the structure of the focus electrode.
One embodiment of the invention provides an electron gun for a cathode ray tube, having a cathode for radiating thermal electrons, control and screen electrodes are disposed away from the cathode at a predetermined distance in respective orders. A focus electrode is disposed away from the screen electrode, the focus electrode having an upper cylinder and a lower cylinder and an inclined portion disposed between the upper and lower cylinders. An anode electrode is formed in a cylindrical shape, the upper cylinder, the inclined portion, and a part of the lower cylinder are disposed in the anode electrode, wherein a length S1 of the upper cylinder in a direction of a tube axis is less than a length T1 of the inclined portion.
The focus electrode in one embodiment is further provided at one end of the upper cylinder with a straight portion.
An inner diameter of the lower cylinder in one embodiment is about 50-65% of an inner diameter of the upper cylinder.
The S1 and T1 in one embodiment are set to satisfy the following equation:
xe2x80x83S1 greater than 2xc3x97T1
An outer diameter of one end portion of the anode electrode in one embodiment is less than that of other portion.
A part of the lower cylinder in one embodiment is disposed in the one end portion of the anode electrode, and the gap between the upper cylinder and the anode electrode is greater than the gap between the lower cylinder and the one end portion.
The anode electrode in one embodiment is provided with an inclined portion corresponding to the inclined portion of the focus electrode.